Karyotypic and loss of heterozygosity analyses demonstrate that the only two known neoplastic Kaposi's Sarcoma [KS] cell lines carry a translocation and/or deletion of chromosome 3p14, indicating involvement of a tumor suppressor gene located at 3p14 in the pathogenesis of KS. We have recently identified and characterized the FHIT gene, a putative tumor suppressor gene on chromosome 3p14.2, site of the translocation present in these two cell lines [KS Y-1 and KS SLK] and have shown that it is altered in several human tumors. We examined the integrity of the FHIT locus in these cell lines by RT-PCR, Souther genomic PCR and Western analyses. Abnormal transcripts as well as DNA rearrangements and/or homozygous deletions were detected in both cell lines, and Western blotting showed that KS Y-1 does not express Fhit protein. In addition, two of four KS primary tumors that we analyzed for alterations in transcription of the FHIT gene, exhibited altered transcripts. Our results indicate that, as had been demonstrated in other solid tumors, the KS lines are heterogenous with respect to FHIT abnormalities, and that FHIT aberrant transcripts in KS tumors result from the presence of DNA lesions in a subset of cells. We hypothesize that altered or absent function of the Fhit protein plays an important role in the development of KS. The role of FHIT gene alterations in KS tumorigenesis in vivo will be determined by Souther blot, RT-PCR and immunohistochemical analyses of KS tumor samples. The precise role of FHIT alterations in KS tumorigenesis will be defined by isolating highly tumorigenic subclones from the KS cell lines and characterizing FHIT rearrangements in the subclones. In this manner we will determine the possible correlation between the presence of particular FHIT rearrangements and the tumorigenic potential of individual subclones. Transfection experiments will be used to restore a normal phenotype to the tumorigenic subclone. These experiments will provide invaluable clues to the genetic mechanisms underlying FHIT-mediated KS pathogenesis.